1. Field of the Invention
The present invention relates to a pneumatic infrared ray detector for use in a gas analyzer detecting infrared rays transmitting through a sample cell and the like to be incident upon a gas chamber.
2. Description of the Prior Art
A pneumatic infrared ray detector for use in a gas analyzer comprises for example a gas chamber, upon which infrared rays transmitting through a sample gas are incident, and a gas chamber, upon which infrared rays transmitting through a reference gas are incident, provided separately, a pair of said gas chambers being communicated with each other through a gas passage, and said gas passage being cut off by means of a vibrating diaphragm of a condenser microphone. And, if there is a difference between said infrared rays incident upon one of the gas chambers and said infrared rays incident upon the other of the gas chambers in quantity, a difference corresponding to said difference in quantity of light is produced between both sides of said vibrating diaphragm in gas pressure, so that, in order to balance these gas pressures, a mechanism for slowly leaking a gas within one of said gas passages cut off by means of the vibrating diaphragm to the other of the gas passages is provided. And, a quantity of said gas slowly leaked becomes an important factor determining a sensitivity and frequency characteristics of said detector, so that it has been required that said quantity of the gas slowly leaked can be controlled in high accuracy.
The pneumatic infrared ray detector for use in a gas analyzer shown in, for example, FIGS. 9, 10 has been known. Referring to FIGS. 9, 10, reference numeral 1 designates a body made of metals and the like provided with a pair of independent gas chambers 2a, 2b, respective opened portions of said gas chambers 2a, 2b, being closed by means of an incident window (not shown) made of infrared ray-transmissive optical material, and a gas being enclosed in the respective gas chambers 2a, 2b. Reference numeral 3 designates a detecting gas chamber provided independently upon the gas chambers 2a, 2b and reference numeral 4 designates a gas passage provided ranging from the gas chamber 2a to a circumferential wall surface of said detecting gas chamber 3 for communicating the gas chamber 2a with the detecting gas chamber 3. Reference numeral 5 designates a gas passage provided ranging from a position distant from a circumferential wall to the gas chamber 2b in a bottom surface 3a of the detecting gas chamber 3 for communicating the gas chamber 2b with the detecting gas chamber 3.
Reference numeral 6a designates a ring-shaped slow leak sheet made from a thin sheet built up on said bottom surface 3a of the detecting gas chamber 3 and an end portion of said gas passage 5 is opened on an inner circumferential side of said ring-shaped slow leak sheet 6a. Reference numeral 8 designates a ring-shaped member built up on the slow leak sheet 6a and a surface brought into contact with the slow leak sheet 6a of said ring-shaped member 8 is roughened. A rough surface of the member 8 is formed by grinding with grinding materials and the like. Reference numeral 9 designates a gas gap formed on an inner circumferential side of the slow leak sheet 6a and the member 8 in their thicknesses. Reference numeral 10 designates a vibrating diaphragm made from a titanium foil and the like composing a condenser microphone built up on the member 8. Reference numeral 11 designates a pressurizing member made from insulating materials built up on said vibrating diaphragm 10, said pressurizing member 11 being provided with a concave portion 12 formed at a central side portion of a surface opposite to the vibrating diaphragm 10 thereof, said concave portion 12 being provided with a gas hole 13 formed in a circumferential portion thereof, and a fixed electrode 14 being fixedly mounted in opposition to the vibrating diaphragm 10.
Reference 15 designates a ring-shaped and wave-shaped plate spring built up on the pressurizing member 11 and reference numeral 16 designates a cover plate. The detecting gas chamber 3 is closed up tight by means of said cover plate 16. The pressurizing member 11, the vibrating diaphragm 10, the member 8 and the slow leak sheet 6a are pressurized through said plate spring 15, respectively, to bring them into close contact with each other at their respective contact surfaces. Accordingly, the gas passages 2a, 2b opened to the detecting gas chamber 3 at one end thereof are cut off by means of the vibrating diaphragm 10. However, a small gap is produced at a contact surface of the slow leak sheet 6a and the member 8 due to said rough surface of the member 8; it is possible to slowly leak the gas in their inner and outer circumferential directions. The plate spring 15 can produce a gas-flowing gap between the pressurizing member 11 and the cover plate 16 and flow the gas in inner and outer circumferential directions of the plate spring 15. Accordingly, of the respective gases enclosed in the gas chambers 2a, 2b, the gas enclosed in the gas chamber 2a arrives at the detecting gas chamber 3 through the gas passage 4 to be filled in the concave portion 12 closed up tight by means of the vibrating diaphragm 10 through said gas hole 13. On the other hand, the gas enclosed in the gas chamber 2b flows through the gas passage 5 to be filled in said gas gap 9 on one side of the vibrating diaphragm 10.
For example, when infrared rays transmitting through a reference gas of a gas analyzer are incident upon the gas chamber 2a and infrared rays transmitting through a sample gas are incident upon the gas chamber 2b, the former is larger in comparison with the latter in quantity of light. Accordingly, the vibrating diaphragm 10 is moved by a pressure resulting from an expansion of the gas enclosed in the gas chamber 2a and thus an electrostatic capacity of a condenser is changed, so that this change in electrostatic capacity is detected. And, upon acting said pressure resulting from said expansion of the gas enclosed in the gas chamber 2a upon the vibrating diaphragm 10 in the above described manner, a difference is produced between a gas pressure in the concave portion 12 on one side of the vibrating diaphragm 10 and that in the gas gap 9 on the other side of the vibrating diaphragm 10. Accordingly, the gas is slowly leaked between the detecting gas chamber 3 and the gas gap 9, as shown by, for example, an arrow in FIG. 9, at a contact surface of the slow leak sheet 6a and the member 8 due to this difference in gas pressure to absorb the difference in gas pressure between both sides of the vibrating diaphragm 10, whereby balancing the gas pressure.
In a slow leak mechanism in the above-described conventional pneumatic infrared ray detector for use in a gas analyzer, the rough surface of the member 8 is brought into contact with the slow leak sheet 6a to produce the gap resulting from the rough surface at the contact surface of the member 8 and the slow leak sheet 6a and these are pressed against each other to control the gap resulting from the rough surface, whereby slowly leaking the gas, that is it is possible to slowly leak the gas. However, the quantity of the gas leaked is controlled by changing a degree of roughness of the rough surface of the member 8, so that it is difficult to control the quantity of the gas leaked consciously in high accuracy. In addition, in the case where this quantity of the gas leaked is controlled to a great extent, it is required to increase said roughness of the rough surface but an increase of the roughness has a limit, so that a problem occurs also in that a range capable of controlling the quantity of the gas leaked is comparatively small.